The Fluorescence-Activated Cell Sorting (FACS) Facility has provided flow cytometry services to AECCC investigators since 1980. This shared resource makes available instrumentation for fluorescence analysis of cell surface and cytoplasmic markers, DNA content, apoptosis, changes in intracellular calcium concentration and for multiparameter cell sorting. The facility also offers computer support for analysis of flow cytometric data and advice on the design and implementation of experimental protocols. At the time of the last CCSG review, the facility was equipped with a FACscan analytic flow cytometer, a FACStar Plus Cell Sorter, and a Zeiss fluorescence microscope. During the current grant period the facility has acquired a second analyzer, the FACS Calibur, and an AutoMACS magnetic cell sorter. A Zeiss inverted fluorescence microscope has also been acquired and a high speed FACS Vantage cell sorter has recently been leased and will be installed shortly. These changes in instrumentation permit the facility to offer analysis of cellular apoptosis, using annexin staining, the TUNEL assay and measurement of DNA content and activation assays that monitor fluxes in intracellular calcium concentration. In addition, the new high speed cell sorter will provide simultaneous analysis of cell populations using up to six fluors and eight parameters simultaneously. The Director of the Facility carries out cell sorting and trains and supervises AECCC investigators, students, fellows, technicians and faculty in the operation of the analyzers and the AutoMACS. The Director maintains the instruments, provides instruction and ensures quality control. This facility is essential for the phenotypic analysis of normal and malignant lymphoid and other cells and for the monitoring of changes in protein expression that accompany activation and transformation of cells of diverse lineages. The high cost of the instrumentation and the need for skilled personnel mandates the availability of a shared resource for flow cytometry. The facility also permits maximum and efficient utilization of the instrumentation. This shared resource represents the only access to flow cytometry and cell sorting within the institution and thus is crucial to AECCC investigators.